In a sense, these studies are looking not at gene-x-environment interactions, or GxE, but at genes x (immediate) environment x culture — GxExC. The third variable can make all the difference. Gene-by-environment studies over the last 20 years have contributed enormously to our understanding of﻿ mood and behavior. Without them we would not have studies, like these led by Chiao and Way and Kim, that suggest broader and deeper dimensions to what makes us struggle, thrive, or just act differently in different situations. GxE is clearly important. But when we leave out variations in culture, we risk profoundly misunderstanding how these genes — and the people who carry them — actually operate in the big wide world.

One of the things I harp on on this weblog is that I see more potential for group selection dynamics at the level of the evolution of culture than the domain of evolutionary genetics. The reasoning is that the power of selection is proportional to heritable variation at the level you’re evaluating. So, of you have two adjacent demes “competing” you’d have to have group-level heritable variation. Basically, the between group component of genetic variation which can’t be reducible to within group variance. Recall that Fst values, the between group component of genetic variance, at the maximal scale of genetic distance is on the order of ~0.15, 15% of the total (the rest being within group). But in real human societies over most of evolutionary history the conflict has been between groups which are genetically much closer, in fact, groups which probably “trade” in women as a byproduct of conflicts or even when at peace, and so diminish extant variation to nearly nothing.

The same issues are not as operative when it comes to culture. Two tribes can speak different dialects or languages. If a woman moves from one tribe to another her children don’t necessarily speak a mixture of languages, rather, they may speak the language of their fathers. The nature of cultural inheritance is more flexible, and so allows for the persistence of more heritable variation at different levels of organization. Differences of religion, language, dress, and values, can be very strong between two groups who have long lived near each other and may be genetically similar.

Over the course of human history our norms may have been shaped by these sorts of cultural dynamics. But over time the norms themselves may have had an impact on the gene frequencies within the populations, as some variants may have been fitter in some cultures than in others. And, within those societies there is still a fair amount of variation and ability to construct “niches,” the “environment” which David speaks of. It’s complex, and I’m glad David is starting the conversation.

On an unrelated note, I find the registration system over at Wired Science a touch onerous. If they want to force registration something which is hooked into twitter or Facebook would be convenient, but as it is, the Ajax was broken on Chrome/Windows 7 for me, in case the tech people are curious. So I never left a comment, which was my intention, because I couldn’t login after registering.

Thanks for the response, Razib, and sorry to hear you got stonewalled at the comments filter at Wired. I’ll pass on the info and fast-track suggestion.

I imagine you’re right about culture permeating more rapidly. I find fascinating though the idea (and evidence) that it has the power to drive genetic change/evolution at a speed we thought unlikely not too very long ago.

I’ll post a comment over there with a pointer here. Thanks for reading and knocking; sorry you couldn’t get in.

Chris T

I find fascinating though the idea (and evidence) that it has the power to drive genetic change/evolution at a speed we thought unlikely not too very long ago.

Evolution and culture can also wind up in a feedback loop. A particular trait is partially genetic and is somewhat favored by a culture. People who are naturally high in that trait produce more offspring and the culture becomes even more favorable towards the trait. Thus you can wind up with a trait that is both favored by genetic and cultural (nature AND nurture).

http://blogs.discovermagazine.com/gnxp Razib Khan

“I thought culture was part of the environment.”

obviously. i think david though was talking about within cultural dynamics as environment.

http://evolvingthoughts.net John Wilkins

I hold to what I call the “Laminar Flow” model of gene/environment/ecology interaction. Rives sometimes have slow moving deep currents, with laminar layers of faster currents as you approach the surface. Culture is rapid, depends to a degree on the deeper currents, but can behave independently of them on occasion.

Culture is what Odling-Smee calls the “niche construction” aspect of the environment. It makes an environment in which genes have fitnesses, where the rest of the environment is more or less passively received. But since culture tends to be rather rapid, the overall effects are ephemeral, usually (some of course aren’t).

As to the group selection point; I think that it only makes sense to talk about group selection relative to some benchmark of individuality, and since each laminar layer has its own dynamics, it also has its own individuals. What is a genetic individual might be an environmental part, or even a sum of parts. Culture constructs its own individuals, so that as a guitarist I am cultural object (or used to be), while as a biological individual my fitnesses are rather better off (two kids, no guitarist career). It pays to keep your focus at the right layer.

It may be that cultural “demes” are in fact individuals; this is what I take Darwin’s point about competing moral tribes in the Descent to be about. Each village is the individual, or rather each moral institution is, and their fitness is the fitness of how many instances of that moral institution are tokened.

http://blogs.discovermagazine.com/gnxp Razib Khan

i was going to refer to “inter-demic ttion”, but i didn’t want to confuse ppl. i like the model btw.

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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com